Extensible boom



1956 s. G. KNIGHT EXTENSIBLE BOQM Filed April 20, 1964 United States Patent 3,264,950 EXTENHBLE BUUM Sidney G. Knight, Schotield, Wis, assignor to Drott Manufacturing Corporation, Milwaukee, Wis, a corporation of Wisconsin Filed Apr. 20, 1964, Ser. No. 363,662 5 Claims. (Cl. 92-51) This invention relates to extensible booms and more particularly to a three-section extensible boom of the type used on mobile cranes and the like.

The subject matter of this application is disclosed and claimed in my copending application, Serial No. 290,108, filed June 24, 1963, and now abandoned.

Extensible booms having three or more telescopically interfitting sections and which are extended or retracted to a greater or lesser extent have been extensively used in cranes and like devices. If the boom is extended by a simple power device connecting the base and end sections there is a tendency for the end section to move to its maximum extended position out of the intermediate section before the intermediate section starts to move out of the base section. This is undesirable because the end section is the smallest and weakest of the sections.

Several different solutions to the problem of properly controlling the boom sections have been proposed. In one mechanism as more particularly disclosed and claimed in my Patent No. 3,112,035 the several boom sections are interconnected by cables for simultaneous and proportional extension and contraction. While the results achieved with this construction are very satisfactory, it is undesirable from the standpoint of cost and difficulty of installation in the space available in some cases to provide cables and sheaves in the boom necessary for its functioning.

Another construction includes latches associated with the boom sections to insure that the end section cannot move out of the intermediate section until the intermediate section has moved to the maximum extent out of the base section. While this construction insures the desired sequence of extension of the boom sections, it cannot positively insure that the end section will be retracted before the intermediate section without unduly complicating the latching mechanism.

It is accordingly one of the objects of the present invention to provide an extensible boom which is relatively simple in construction, which can easily be installed in the available space, and which will insure the desired sequence of movement of the boom sections during both extension and retraction.

Another object is to provide an extensible boom in which the several sections are individually moved during both extension and retraction by fluid cylinder and piston units which are proportioned to produce the desired sequence of movement.

According to a feature of the invention, two cylinder and piston units are provided in a compact assembly in which the tubular piston rod for the larger unit provides the cylinder for the second and smaller unit.

The above and other objects and features of the invention will be more readily apparent from the following description when read in connection with the accompanying drawing, in which:

PEG. 1 is a side elevation with parts in section of an extensible boom embodying the invention; and

FIG. 2 is a section through the power unit for extending and retracting the boom.

The complete boom, as shown in FIG. 1, comprises an outer tubular section which is provided at one end with a pivot mounting 11 for pivotally mounting it on a mast or base as, for example, on a mobile unit. The base section is adapted to be swung in a vertical plane about the pivotal mount 11 for which purpose an exatented August 9, 1966 "ice P tensible cylinder may be connected to a bracket 12 on the base section. The exact manner of mounting the boom and of causing it to swing about its mounting forms no part of the present invention and will not be described in further detail.

The outer base section also carries a drum, indicated at 13, on which a cable may be wound and which drum may be driven by suitable motor means, such as a hydraulically operated motor. The cable from the drum may extend over a sheave in an end block member 14 carried by the end of the boom with the cable extending down to a suitable hook or similar material engaging device. The base section may be formed with guards, such as 15, partially enclosing the cable and enclosing or partially enclosing the sheave and operating motor therefor.

The base section telescopically receives a tubular intermediate section 16. Preferably bearings, as shown at 17 and 18, are provided at the rear and forward ends of the intermediate section and base section slidably to support the intermediate section in the base section for telescopic movement. A third end section 19 is similarly telescopically fit into the intermediate section 16 with bearings 21 and 22 being provided to support the end section. The block 14 is mounted at the outer end of the end section to be supported thereby so that it will be moved toward and away from the pivotal mounting of the base section as the boom is extended and retracted.

The intermediate and end sections are adapted to be moved telescopically outwardly and inwardly by a compound fluid motor indicated generally at 23 and which is preferably mounted within the tubular end section 19. The fluid motor 23 includes a first piston rod 24 and a second or inner piston rod 25 projecting from the forward end thereof, as seen in FIG. 1. The first piston rod 24 is connected at its outer end to a sleeve 26 surrounding the fluid motor and lying radially within the end tubular section 19. At its rearward end the sleeve 26 is connected through an annular ring 27 to the inner end of the intermediate boom section 16, as shown. Therefore, when the first piston rod 24 is moved outwardly of the fluid motor it will act through the sleeve 26 and annular ring 27 to move the intermediate boom section 16 in the base section. The inner piston rod 25 is secured through an end coupling 28 to the outer end of the end section 19. As shown, the end coupling 28 projects through a mounting plate 29 secured in the end of the end section and to which the block 14 is mounted with a pin 31 securing the end coupling to the end fitting.

The compound fluid motor 23, as best seen in FIG. 2, comprises an outer elongated cylinder 32 closed at its rearward end by an end plate 33 and open at its forward end. A piston 34 is slidable in the cylinder 32 and is formed with an elongated tubular piston rod 24 extending through the front end of the cylinder. Preferably, a sealing gland 36 secured in the front end of the cylinder seals against the piston rod 24 and provides a bearing therefor.

The elongated piston rod 24- forms a second cylinder of smaller diameter than the outer cylinder 32 in which a second piston rod 25 is secured to the piston 37. The piston rod 25 projects through a sealing gland 38 in the forward end of the piston rod 24 to seal against the piston rod 25 and to provide a bearing therefor. The piston rod 25 is preferably also tubular, as shown, and is secured directly to the end coupling 28.

Actuating fluid is supplied to the rear end of the outer cylinder 32 through a fluid connection 39 to urge the piston 34 forwardly in the outer cylinder 32. The piston 32 is formed with a passage 41 therethrough so that when fluid is admitted to the rear end of the cylinder 32 it will also flow through the passage 41 into the rear end of the cylinder 24 to act simultaneously on the rear end of the smaller piston 37. The space between the cylinder 32 and the piston rod 24 forwardly of the piston 34 communicates with a fluid conduit 42. The piston 34 is formed with a passage 43 communicating with this space and also with a tube 44 secured to the piston 34 and extending forwardly therefrom. The tube 44 extends slidably through the piston 37 and into the hollow piston rod 25, as shown. Preferably stop sleeves 45 and 46 are secured to the pistons 34 and 37, respectively, to limit their forward travel.

In use when it is desired to extend the boom fluid under pressure is supplied to the connection 39 and the connection 42 is supplied to exhaust. Thus, high pressure acts on both the pistons 34 and 37 tending to urge them to the right, as seen in FIG. 2, to extend the boom. The piston rod 24 being connected to the intermediate boom section 16, as described above, will urge it outwardly of the base section and the inner piston rod 25 being connected to the end boom section 19 will urge it outwardly of the intermediate boom section.

With the construction as shown the boom sections can be caused to extend and retract in any desired sequence. According to the preferred sequence, the piston 34 is made sufficiently larger than the piston 37 to insure that the intermediate boom section 16 will be fully extended from the base section 10 before the end section 19 starts to move out of the intermediate section. This can easily be accomplished by proportioning the piston areas despite the fact that more force is required to move the intermediate section than to move the end section. On retraction the relative annular areas of the pistons 34 and 37 are so proportioned by adjusting the relative sizes of the cylinders 32 and 24 and piston rod 25 that the end boom section will be fully retracted into the intermediate section before the intermediate section starts to retract into the base section. Thus, under no condition can the smaller, weaker end section be extended when the larger, stronger intermediate section is retracted.

According to another desirable sequence of operation, the intermediate and end sections would be extended simultaneously and proportionately to maintain the hearing loads thereon balanced. For this purpose the areas of pistons 34 and 37 should be proportioned according to the force required to move the intermediate and end sections respectively. Therefore, when the same fluid pressure is applied to extend the boom, the intermediate and end sections would tend to move simultaneously and proportionately. If one section, say the end section, should be extended first, its bearings would move relatively closer together and would be subjected to a relatively higher bearing load. Therefore, there would be a relatively greater load and relatively greater friction on the end section bearings than on the intermediate section bearings and the intermediate section would tend to move proportionately to movement of the end section. In this way, the bearing loads between adjacent sections would be maintained substantially in balance so that the sections occupy the optimum relationship relative to each other of which they are capable at all times.

While simultaneous and proportional extension of the intermediate and endsections is very desirable, it is difficult to achieve in practice. In the first place the areas theoretically required for the various parts may calculate out to odd sizes which are uneconomical and impractical in commercial practice. Furthermore it is a practical impossibility to maintain all of the bearings so mounted and lubricated as to produce the same coefficient of friction.

To insure that, in practice, the end section will never move out before the intermediate section the sizes of the pistons and tubular piston rods are selected to the nearest standard size such that the intermediate boom section will always tend to be moved out before the end section and the end section will always be retracted before the intermediate section.

The action may vary somewhat depending upon the exact relationship of the coefficients of friction of the bearings. In most cases the intermediate section will be extended to its full or substantially full extent before the end section moves at all, but it is possible that under some conditions, after movement of the intermediate section through only a relatively short distance, the end section could start to move and the two sections could then continue to move simultaneously. On retraction, the end section will always start in first and will continue until it is fully retracted before the intermediate section starts to move. This is because the relative piston areas are selected to insure this operation. Also, once the end section starts to move, loads on the end section bearings will be decreasing due to greater separation between them while the spacing between the intermediate section bearings is not changing.

While one embodiment of the invention has been shown and described herein, it will be understood that it is illustrative only and not to be taken as a definition of the scope of the invention, reference being had for this purpose to the appended claims.

What is claimed is:

1. An extensible boom for cranes and the like comprising a tubular base section, a tubular intermediate section telescopically slidable in the base section, tubular end section telescopically slidable in the intermediate section, and a pressure responsive power unit lying within the end section when the boom is retracted and expansible and contractable to extend and retract the boom, the power unit comprising an outer cylinder, a piston having a tubular elongated piston rod slidable in the outer cylinder and said piston rod defining an inner cylinder of smaller diameter than the outer cylinder, a second piston in the inner cylinder having an elongated piston rod, means connecting the outer cylinder and the second piston rod to the base section and the end section respectively, means lying radially between the outer cylinder and the tubular end section connecting the outer end of the first piston rod to the inner end of the intermediate section, and means simultaneously to supply actuating fluid under pressure to the same ends of the cylinders and to connect the other ends of the cylinders to exhaust.

2. The extensible boom of claim 1 in which the areas of the cylinder and piston units are so proportioned that the intermediate section will be extended from the base section before the end section is extended from the intermediate section and the end section will be retracted into the intermediate section before the intermediate section is retracted into the base section.

3. An extensible boom for cranes and the like comprising a tubular base section, a tubular intermediate section telescopically slidable in the base section, a tubular end section telescopically slidable in the intermediate section, and a pressure responsive power unit lying within the end section when the boom is retracted and expansible and contractable to extend and retract the boom, the power unit comprising an outer cylinder, a piston slidable in the cylinder, a tubular piston rod connected to the piston and extending through the forward end of the cylinder, and defining a second cylinder, a second piston slidable in the second cylinder and having a second piston rod extending through the forward end of the first piston rod, a connection from the first cylinder to the base section, a sleeve surrounding the outer cylinder within the end section connecting the [forward end of the first piston rod to the rearward end of the intermediate section, a connection from the forward end of the second piston rod to the forward end of the end section, and means simultaneously to supply actuating fluid under pressure to the same ends of the cylinders.

4. An extensible boom for cranes and the like comprising a tubular base section, a tubular intermediate section telescopically slidable in the base section, a tubular end section telescopically slidable in the intermediate section, and a pressure responsive power unit lying within the end section when the boom is retracted and expansiible and contractable to extend and retract the boom, the power unit comprising an outer cylinder, 21 first piston slidable in the outer cylinder, at first tubular piston rod of smaller diameter than the first piston connected to the first piston and extending through the forward end of the outer cylinder and defining a second cylinder, 21 fluid seal between the forward end of the outer cylinder "and the first piston rod, a second piston slidable in the second cylinder, a second tubular piston rod of smaller diameter than the second piston extending through the forward end of the second cylinder, connections between the outer cylinder and base section, the outer end of the first piston rod and the inner end of the intermediate section, and the second piston rod and the end section, the connections between the first piston rod and the intermediate section being elongated and lying radially between the outer cyl- References Cited by the Examiner UNITED STATES PATENTS 2,43 8,285 3/ 1948 Houldsworth 92-51 2,961,837 11/1960 Suderow 6146.5

FOREIGN PATENTS 588,938 2/ 1959 Italy.

EDGAR W. GEOGHEGAN, Primary Examiner.

SAMUEL LEVINE, Examiner.

0 I. C. COHEN, Assistant Examiner. 

1. AN EXTENSIBLE BOOM FOR CRANES AND THE LIKE COMPRISING A TUBULAR BASE SECTION, A TUBULAR INTERMEDIATE SECTION TELESCOPICALLY SLIDABLE IN THE BASE SECTION, TUBULAR END SECTION TELESCOPICALLY SLIDABLE IN THE INTERMEDIATE SECTION, AND A PRESSURE RESPONSIVE POWER UNIT LYING WITHIN THE END SECTION WHEN THE BOTTOM IS RETRACTED AND EXPANSIBLE AND CONTRACTABLE TO EXTEND AND RETRACT THE BOOM, THE POWER UNIT COMPRISING AN OUTER CYLINDER, A PISTON HAVING A TUBULAR ELONGATED PISTON ROD SLIDABLE IN THE OUTER CYLINDER AND SAID PISTON ROD DEFINING AN INNER CYLINDER OF SMALLER DIAMETER THAN THE OUTER CYLINDER, A SECOND PISTON IN THE INNER CYLINDER HAVING AN ELONGATED PISTON ROD, MEANS CONNECTING THE OUTER CYLINDER AND THE SECOND PISTON ROD TO THE BASE SECTION AND THE END SECTION RESPECTIVELY, MEANS LYING RADIALLY BETWEEN THE OUTER CYLINDER AND THE TUBULAR END SECTION CONNECTING THE OUTER END OF THE FIRST PISTON ROD TO THE INNER END OF THE INTERMEDIATE SECTION, AND MEANS SIMULTANEOUSLY TO SUPPLY ACTUATING FLUID UNDER PRESSURE TO THE SAME ENDS OF THE CYLINDERS AND TO CONNECT THE OTHER ENDS OF THE CYLINDERS TO EXHAUST. 